6 sensation Somatic senses Mechanoreceptive somatic senses Stimulated by mechanical compression or stretching of some tissue of the bodyTactile senseTouch , pressure, vibration , tickle sensesposition senseStatic position and rate of movement sensesThermoreceptive sensesDetect heat and coldPain senses
7 sensation Sensory pathway: 1st : enters spinal cord from periphery 2nd : crosses over (decussates), ascends in spinal cord to thalamus3rd : projects to somatosensory cortex
11 Spinothalamic pathway FunctionCarries pain, temperature, crude touch and pressure signals (superficial sensations)Three-order neuron1st order neuron enters spinal cord through dorsal root2nd order neuron crosses over in spinal cord; ascends to thalamus3rd order neuron projects from thalamus to somatosensory cortex
12 spinothalamicpathwayPain , temperature, crude touch and pressure signals
14 Spinothalamic damage spinothalamic pathway spinal cord injury Loss of sense of (superficial sensations):crude TouchPainWarmth/coldin right leg
15 Dorsal column pathway Function Three-order neuron Carries fine touch, vibration and conscious proprioception signals(deep sensations)Three-order neuron1st order neuron enters spinal cord through dorsal root; ascends to medulla (brain stem)2nd order neuron crosses over in medulla; ascends to thalamus3rd order neuron projects to somatosensory cortex
16 dorsalcloumnpathwayfine touch, vibration and conscious proprioception signals
21 Differences between the two system VelocitiesThe dorsal column–medial lemniscal system: large, myelinated nerve ﬁbers30 to 110 m/sec,The anterolateral system :smaller myelinated ﬁbersa few meters per second up to 40 m/sec.
22 Differences between the two system spatial orientation : in spinal cordthe dorsal column–medial lemniscal system :high degree of with respect to their originthe anterolateral system : much less spatial orientationlower parts of the body---center of the cordhigher parts---lateral layers
23 Spinocerebellar pathway Function :receives inputs from golgi tendon organs and muscle stretch receptors. proprioception signalsReceptors : muscles & jointsThree-order neuron1st order neuron: enters spinal cord through dorsal root2nd order neuron: ascends to cerebellum3rd order neuron to cortexThe ventral spinocerebellar tract conveys proprioceptive information from the body to the cerebellum. It is part of the somatosensory system and runs in parallel with the dorsal spinocerebellar tract. Both these tracts involve two neurons. The ventral spinocerebellar tract will cross to the opposite side of the body then cross again to end in the cerebellum (referred to as a "double cross"), as compared to the dorsal spinocerebellar tract, which does not decussate, or cross sides, at all through its path.
24 Spinocerebellar pathway DivisionPeripheral Process of First Order the NeuronRegion of Innervationdorsal (posterior) spinocerebellar tractfrom muscle spindle (primarily) and golgi tendon organsIpsilateral Caudal Aspect of the body and legsventral (anterior) spinocerebellar tractfrom golgi tendon organsThe ventral spinocerebellar tract conveys proprioceptive information from the body to the cerebellum. It is part of the somatosensory system and runs in parallel with the dorsal spinocerebellar tract. Both these tracts involve two neurons. The ventral spinocerebellar tract will cross to the opposite side of the body then cross again to end in the cerebellum (referred to as a "double cross"), as compared to the dorsal spinocerebellar tract, which does not decussate, or cross sides, at all through its path.
25 Dorsal column damage Sensory ataxia (loss of coordination) Patient staggers; cannot perceive position or movement of legspartially compensated by visual surveillanceataxia [英] [ə‘tæksiə] 共济失调
26 Spinocerebellar tract damage Cerebellar ataxiaa failure of the fine coordination of muscle movementsClumsy movementsIncoordination of the limbs (intention tremor)Wide-based, reeling gait (ataxia)Alcoholic intoxication produces similar effectsreeling gait 步态蹒跚
27 "inner chamber” in Greek thalamusanterolateral view"inner chamber” in Greek
32 thalamus 2 Associated nuclei Receive their driving inputs from Other cortical areasventral-lateral nucleuscerebullum ,globus pallidus—motorPulvinar nucleusMedial ,lateral geniculate--sensorsventral lateralpulvinar nucleus
33 thalamus 3 nonspecific projection nucleus “nonspecific nuclei”connect to association areas of cortex and/or limbic structure.Anterior nucleiMedial nucleiIntralaminar and reticular nucleilimbic structureintralaminar reticularnonspecific projection nuclei: Dispersion in projection
36 Projection system of thalamus Reticular formation
37 Projection system of thalamus FunctionSpecific projection system of thalamusSpecific senses: visual or auditory cortex (except olfaction)Non-specific projection system of thalamusMaintain and alter the excitatory situation of cortex
42 Somatosensory cortex Cross projection Each side of the cortex receives sensory information exclusively from the opposite side of the body (the exception: the sensor information from face is bilateral projection).exclusively
43 Somatosensory cortexThe finer the sense, the larger the somato-sensory cortex areaThe lips, face and thumb are represented by large areas in the somatic cortex, whereas the trunk and lower part of the body, relatively small area.exclusively
44 Somatosensory cortex Inversely projection “Up is down and down is up ” The head in the most lateral portion, and the lower body is presented medially.exclusively
57 Visceral pain Poorly localized; may be “referred” Slow pain Mostly caused by distension of hollow organs or ischemia (localized mechanical trauma may be painless)
58 Visceral painAgina:due to ischemia of the heart muscle, generally due to obstruction or spasm of the coronary arteries.
59 Refered painis pain perceived at a location other than the site of the painful stimulusSite of pain may be distant from organumbilicus
60 Visceral pain myocardial infarction : (heart attack), where pain is often felt in the neck, shoulders, and back rather than in the chest, the site of the injury.
61 Mechanism of refered pain Convergence theoryThe primary afferent axons of skin and viscera converged on the same interneurons in the pain pathways.
62 Mechanism of refered pain Convergence theoryThis theory explains why referred pain is believed to be segmented in much the same way as the spinal cord. Fail to explain why there is a delay between the onset of referred pain after local pain stimulation. Threshold for the local pain stimulation and the referred pain stimulation are different, but according to this model they should both be the same.
63 Mechanism of referred pain Facilitated theoryThe primary afferent axons of skin and viscera closed to each other
64 Mechanism of referred pain Facilitated theoryto explain why there is a delay between the onset of referred pain after local pain stimulation.
65 Summary Spinothalamic pathway Dorsal column pathway Specific projection systemNon-specific projection systemSensory area of cerebral cortexReferred pain